1. Field of the Invention
This invention relates to the field of plastic coatings and particularly to the field of flame-resistant plastic coatings.
2. Description of the Prior Art
Many structures such as fiberboard or cardboard containers have poor flame resistance. Although their flame resistance can frequently be improved by incorporating additives in the fiberboard formulation, these additives generate toxic volatiles when pyrolyzed. Insulative foam can be attached to the exterior of such structures, but the large volume of the foam reduces the useful space.
Another approach used to improve the flame resistance of structures is to paint them with intumescent coatings. These are paints which contain an intumescing agent. When heated, the paint expands and insulates the structure from the flame by increasing the distance between the flame and the surface of the structure. One intumescent paint which has been reported (NASA Tech Briefs, Summer 1979, page 224) has a fluorocarbon latex resin base plus a pigment and miscellaneous additives. This waterbased paint has approximately 40% of an intumescing agent such as sulfanilamide, melamine pyrophosphate, or polysulfonamide derivatives of polycyclic aromatic compounds.
Prior art intumescent coatings suffer from one or more of several shortcomings. In some cases, a toxic gas is generated during intumescing which increases the hazard to persons present during a fire. Frequently the efficiency of the coating decreases in the presence of moisture because of the ionic character of the intumescent agents used. Additionally, the expanded coating may be weak and friable, causing it to erode rapidly from the structure's surface by the impinging flame and hot gases.